Huh? Higher octane fuel burns slower and has less energy per gallon than low octane fuel. Because it resists predetonation more than low octane fuel, it is typically used in high compression ratio engines that generate more power per turn of the crank compared to their displacement by virtue of having the higher compression ratio.
The theory, at least, is that due to the thinner air, gasoline is less likely to predetonate when compressed at high altitudes, so you can get away with a lower octane rating. Just don't try it in a turbocharged engine, because turbos are very efficient at producing a similar manifold absolute pressure as at sea level when you're up at altitude, which would result in knocking.
Yeah... sorry meant burns faster... not slower... which is why I thought econ would go down... but this wasn't the case in the mountains... I always thought higher octane meant more energy... but clearly I am wrong...
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